An electromagnetic contactor generates an attraction force to attract a movable iron core to a stator iron core through energization of an operation coil constituting an electromagnet device to cause a movable contact to contact/separate from a fixed contact. This opens and closes an electric circuit between a single-phase power supply and a three-phase power supply and a load device.
Conventionally, coil driving circuits used for the electromagnetic contactor have been variously proposed (for example, see PTLs 1 to 3).
PTL 1 discloses a coil driving device of an electromagnet that includes a semiconductor switching element, which supplies an operation coil with a power supply voltage, a voltage detection circuit, which detects the power supply voltage, a gain circuit, which outputs an input level signal according to the detection voltage by this voltage detection circuit and outputs a holding level signal higher than the input level signal based on the detection voltage after a set period, a reference wave generating circuit, which generates a sawtooth wave, a comparator, which compares the sawtooth wave from this reference wave generating circuit with the input level signal from the gain circuit, compares the sawtooth wave with the holding level signal after an elapse of an output setting period of an input pulse signal at a fixed cycle, and outputs a holding pulse signal with an on/off time ratio (also referred to as a duty ratio) smaller than that of the input pulse signal, and a pulse output circuit, which supplies this input pulse signal from the comparator and the holding pulse signal to the semiconductor switching element.
That is, this PTL 1 discloses the following technology. Since a large attraction force is required in a close circuit control in which an iron core gap of the electromagnet is large (that is, a fixed contact point is separated from a movable contact point), a coil is excited at a large current. Meanwhile, in a holding control in which an iron core enters an attracted state and an iron core gap is absent, since maintaining the attracted state is possible even if the operation coil is excited at a comparatively small current, a coil current is reduced as much as possible to lower the electric power consumption.
PTL 2 discloses the following technology. An integrating circuit constituted of a capacitor and a resistor integrates a voltage applied to an operation coil during driving of an electromagnetic relay. After an elapse of a period according to a time constant of the integrating circuit, the applied voltage is lowered to lower electric power for the operation coil driving. The integrating circuit here performs the integration with the capacitor to which the applied voltage to the electromagnetic relay is arbitrarily set and the resistor. The integrating circuit is not a circuit to detect the operation of the operation coil of the electromagnetic relay but is a timed circuit to set the period from the applied voltage to the operation coil.
PTL 3 discloses an electromagnet device that includes switch means, which flows an exciting current to an operation coil when a power supply voltage at a start of power-on exceeds a determination value, detecting means of the exciting current, a timer circuit for an operation setting time in inverse proportion to a magnitude of the power supply voltage, which starts operating when the detection value by this detecting means exceeds the determination value, and means, which controls the switch means after an elapse of the operation setting time by this timer circuit to flow a holding operation current to the operation coil.
That is, conventional examples described in PTL 3 describes (1) a technology that controls a voltage to be in inverse proportion to a switching period from power-on to the holding state such that the switching period becomes short while the applied voltage is high and the switching period becomes long such while the applied voltage is lowered to reduce an impact during the application of the power supply, (2) a technology that measures an impedance of the operation coil to determine timing at which the operation coil of the electromagnetic contactor is switched to the holding operation and controls the operation to the operation coil holding operation when the impedance increases and the electromagnet attracts, and (3) a technology that prepares a high-frequency power supply to apply a high-frequency voltage to a coil different from a coil of operation coil driving to measure the operation coil impedance, and measures a current flowing through the operation coil by this high-frequency voltage to measure the impedance of the operation coil from a change in high-frequency current.